An extension cord with 2 male ends is called a suicide cord for a good reason. Don't do it.

Thank you for your reply! Can you elaborate a little further?
The alternative is That I disconnect the furnace wiring at the receptacle and connect that to a male three prone plug and plug it to a generator.

If I turn off the furnace circuit breaker, doesn't the two male end extension cord perform the same function?

Thank you for your reply! Can you elaborate a little further?
The alternative is That I disconnect the furnace wiring at the receptacle and connect that to a male three prone plug and plug it to a generator.

If I turn off the furnace circuit breaker, doesn't the two male end extension cord perform the same function?

For a temporary solution it will work, but you want to get it wired up properly as soon as you can. At my house I pull the main breaker out and replace it with another one wired up to my generator. Then I just turn off the breakers to the things I don't need powered up. By pulling the main breaker I don't have to worry about back feeding the power.

Thank you, insteng! Yes, this is only temporary and only as last resort to prevent water pipe busting and being frozen to death:-(.

Just to double check, you are talking about using two male plug extension cord, right?

Yes, use the two male plug extension cord. Make sure your breakers are turned off to prevent backfeeding. You will want to plug it into the outlet first then plug it into your generator. That way you don't have a live wire hanging out where you might accidently touch it if you plugged it into the generator first.

Seriously, google suicide cord. Don't do it.
Sure, if you do everything properly it'll work. But if you get distracted for a brief moment, it could easily result in you getting electrocuted or, even worse, you could kill someone else with it.

I know ... I know ... you'll always do everything in a regimented step by step fashion and you'll never screw up. And it's only temporary. You'll definitely not forget to install a proper lockout before the next time. It's only this once.

This question has been asked several times over the time that I've been visiting this site. The arguments have already been written. Search the forum for previous threads.

Do it properly so that you don't have to worry about it. It isn't that expensive.
Or just get some baseboard heaters and plug them into your generator. If it's only a temporary emergency matter, that's good enough.

I disconnect the furnace wiring at the receptacle and connect that to a male three prone plug and plug it to a generator

And that is a WAY safer way of doing it. No chance of backfeeding the panel and there are never live exposed prongs.
It probably isn't legal according to the code (I'm sure an electrician will jump in and clarify this issue) because the wire that is being used isn't designed to be used that way.
If there is absolutely no way that you will be convinced to do it the proper way, please do it this way instead of the suicide cord.
But I still suggest doing it the proper way.

I don't know of anything (code or otherwise) that precludes putting a cord and plug on a furnace unless the manufacturer specifically says not to. It certainly makes the movement from the house power to the generator safe and straightforward.

I guess I was assuming that she was going to put the plug onto the end of the NM cable. Would that be a violation?

Does she have to transition from the NM cable to some kind of proper cordage for this to be allowed?

Proper cordage, sure, It is not going to be inexpensive so you might want to make the transition as close to the genset as practical. If I were to do this near the furnace and I wanted to make it more robust, I would buy a junction box and use a strain relief of some sort to enter it with some cord that is used for generators. I'd pull out the cable for the furnace and enter the same box with a clamp. Wire nut the connections, cover the box, fasten it down and I'd be good to go.

My only question is what is the safest way to handle the ground. Would one want to connect only to the generator ground and should that be connected to a ground electrode system, or would you connect to the existing ground conductor for the furnace that runs back to the main, building electrode. What goofs me up is that the furnace (or boiler) is not independent from the building even though you can disconnect the existing ground. The furnace or boiler may be connected to metal that runs to every part of the building.

Just install a 30 amp inlet at the panel and an interlock kit. It is safe, legal and code compliant. The materials for this install are not more than $200. A small price to pay for SAFE heat in a power outage.

Sara,

After seeing your message on the fruit forum, I decided to come over and see what you've got going on. Hope I'm not intruding on this forum.

It looks like you have your answer. Namely, disconnecting the furnace, attaching a pigtail to the furnace and plug it in the genset.

You could also attach a permanent pigtail to the furnace, add a box with a duplex receptacle (wired to a dedicated circuit for your furnace) and plug your furnace into the recep when the power is on. When using backup power, you can simply unplug the furnace from the recep and plug it into your generator (with a good quality extension cord). This is not code compliant for a non-portable furnace, but it is vastly safer than a suicide cord.

The problem with a suicide cord and opening the main breaker is that you may be able to manage it, but sometimes others may not. All it takes is for someone to go down and flip the main back on (possibly checking to see if the power is back on before unplugging the generator) and someone could die. It's happens. Of course the homeowner can be subject to criminal prosecution.

The other thing to consider is that even if you are careful enough to keep a lineman from being electrocuted, if someone else on the same line killed a lineman with his generator, you could be blamed, even if it wasn't your fault.

What I ended up doing in my house was installing a subpanel off the main, with a double throw transfer switch in between. I needed a subpanel anyway and the transfer switch was cheaper because I only needed one the size of my subpanel (100A). I would have needed a 200A if I had used it to switch the main. With the transfer switch in between the main and sub panel, there is no possibility of back feeding. It's also code compliant.

Of course my set up won't run the whole house on back-up but I put all my "critical" circuits in the sub. Stuff like a dedicated microwave circuit (so I can cook some food) deep freeze, refrigerator, various rooms, garage lights, etc.

A lot of people use an interlock on their main, which is probably the cheapest route. I think those are less than 100 bucks.

One last thing to think about is your generator. Some smaller generators produce very poor quality electricity. They can severely shorten the life of electronics. In other words, it could cook the board in the furnace. Keeping the generator lightly loaded helps produce cleaner power.

Inverter generators produce the cleanest power (good sine wave, stable voltage).

Good luck and may your power stay on.

This post was edited by olpea on Fri, Feb 14, 14 at 1:26

"This is not code compliant for a non-portable furnace"

Your advice is spot on, but I disagree that a plug and cord connected furnace is not compliant. Could you cite the article?

I hope Sara saw all of these replies and didn't end up killing herself by following insteng's advice.

Thank you everybody for the lively discussion! I was helping hubby battling the deep snow around the house yesterday and didn't get around to post back.

First, a quick update. We didn't lose power at all, so I didn't even have a chance to use the suicide cord to commit suicide:-).

Let me post this quick note to let everybody know that I am ok. I will write more later today, I have some follow up questions so be sure to check back.

Happy Valentine's day!

Thank you very much for all your help!

If the main panel can accept an interlock, btharmy's suggestion is clearly the most reasonable solution.

Actually olpea's suggestion is the most reasonable and economical. Disconnect the furnace hardwire in the back of the receptacle, install a plug and plug it into the receptacle. Done. Next time the power is out unplug from receptacle and plug into a standard extension cord to the generator.

"Your advice is spot on, but I disagree that a plug and cord connected furnace is not compliant. Could you cite the article?"

Hi Joe,

Marknmt over on the fruit and orchards forum mentioned your a regular here. He mentioned you in the context of some "exceptionally well-qualified posters". This is my first time on this forum.

I don't have an NEC book, but apparently 422.16 Flexible Cords says:

"(A) General. Flexible cord shall be permitted (1) for the
connection of appliances to facilitate their frequent interchange or to prevent the transmission of noise or vibration or (2) to facilitate the removal or disconnection of appliances that are fastened in place, where the fastening means and mechanical connections are specifically designed to permit ready removal for maintenance or repair and the appliance is intended or identified for flexible cord connection." (Emphasis added)

Admittedly, there is a small amount of interpretation needed, so it's possibly not crystal clear (I suppose one could argue a stationary furnace is intended for flexible cord) but I think following the NEC to the letter would mean no pigtail on a furnace.

Cord and plug furnace hookup is mentioned with a few passing comments on Mike Holt's forum (see below on page 3 and page 4) in the context of a larger discussion on whether or not furnaces require afci or gfci protection.

Personally it seems such a small infraction I wouldn't try to dissuade someone from installing a pigtail on their furnace, as long as the outlet was dedicated. It seems to me a reasonable compromise for a homeowner to provide the basic necessity of heat during a winter power outage with a small portable generator. I'm not saying I recommend it, just that I wouldn't dissuade the idea. I would still recommend opening the main breaker when using a portable generator in this fashion.

Here is a link that might be useful: Furnace wiring

Just want you all to know that I couldn't find an electrician who is willing to put an interlock on the main panel. When I first got the generator last summer, I called quite a few electricians. They all wanted put transfer switch in, but when I pursued interlock option, they all disappeared:-(. I like interlock because the flexibility it gives me, not to mention the cost advantage:-)

I even figured out the model of my panel and what kind of interlock kit to buy.

Anyone can recommend a electrician who is willing to install an interlock? I live at western suburb of Philadelphia city.

I believe that we've seen discussions like this before on this forum. Don't NEC rules end at the receptacle?

If so, any safety issues reside with the safety-certifying entity that approved the furnace.

If that is all true, the user does not really need either the NEC or the furnace-certifying body to do what they want with their equipment. I can plug in any darned thing that I want. It may, or may not be a smart thing to do, but it is my call.

Was the interlock made by the panel manufacturer? If aftermarket, it may not be approved by the appropriate body for safety in that panel. That may be why the electricians refused to mess with them and local inspectors won't approve them. If the latter is true, after the word gets out to electricians, they surely will stop using them. I would think that the electricians might mention that to homeowners.

Here is a link that might be useful: After market interlocks

Ionized, i never got as far with electricians as who manufactures the interlock. Quite a few claimed they don't know anything about interlock kit, some said they will get back to me, but they never did.

Is it because they don't make as much money installing interlock?

I was on the same website your link referred to and found a resaler a few hours away from me. He wouldn't give me name of any electrician who buys interlock from them. Even if he did, it was too far from me anyway.

So, the interlock kit from that website is ok if I find the right model?

Better to get the one for your panel if there is such a thing. Go get the model number and whatnot off your panel and check with the manufacturer. You can check with the electrical equipment suppliers in your area or the manufacturer web site. If you get frustrated, post back here and maybe someone can help.

"Don't NEC rules end at the receptacle? ......If that is all true, the user does not really need either the NEC or the furnace-certifying body to do what they want with their equipment. I can plug in any darned thing that I want. It may, or may not be a smart thing to do, but it is my call."

Ion,

I completely agree. If I wanted a pigtail on my furnace, I'd put one on.

That said, since NEC covered it in two articles, I think it's fair to say they think it falls under their jurisdiction.

400.7 (A)(8) says

" Uses Permitted
(A) Uses. Flexible cords and cables shall be used only for the following:
(8) Appliances where the fastening means and mechanical connections are specifically designed to permit ready removal for maintenance and repair, and the appliance is intended or identified for flexible cord connection."

I certainly didn't come up with this interpretation on my own. If you Google it on other forums you'll find some inspectors won't approve a pigtail on a furnace (over the top picky in my opinion). I stumbled across one electrician who wrote, "I have also heard an inspector say 'do you think the tenet is going to slide out the furnace and vacuum behind it?'"

Mike Holt wrote an article discussing cords and fixture wires (full article linked below). The article starts out, "Don't underestimate the requirements for flexible cords and fixture wires. They are important enough that the NEC covers them in two separate articles. Specifically, you'll find flexible cord requirements in Article 400 and fixture wire requirements in Article 402."

He goes on to say, "In [400.8], you'll find a list of 6 uses not permitted for flexible cords. Consider the first item: you can't use cords to substitute for the fixed wiring of a structure-that's Chapter 3, again."

I'm sure Ion is aware of Mike Holt's credentials, but for others, Mike Holt is a certified electrical instructor and nationally recognized as a leading expert in interpreting and teaching NEC guidelines and electrical theory. He also submits proposals and comments to NEC code making panels.

All that said, I think installing a furnace pigtail is such a small infraction, it's hardly worth worrying about, IMO. I like what one electrician on a forum said, "It's a trifling violation at worst, right up there with taking tags off of mattresses."

If an inspector did flag a furnace pigtail it could be hard wired back easily enough.

Here is a link that might be useful: Cords and Fixture Wires - Mike Holt

The interlock kit I installed did not require an electrician to install. It required the skills of someone familiar with a power drill and a screwdriver.

Installing the outside box, wiring and breaker into the panel would require an electrician. It might require moving some circuits in the panel to make room for the generator breaker in the upper right. In my case, I was fortunate to have an empty space in that location.

There is also a device that can be attached between the meter and the meter base which accepts a 30amp generator cord. An advantage is that it will automatically switch over to line power when service is restored. It's a bit pricey but it can be installed in minutes.

Here is a link that might be useful: interlock kit

"The interlock kit I installed did not require an electrician to install. It required the skills of someone familiar with a power drill and a screwdriver."

That's kind of what I was thinking but didn't want to say so on the public forum. A lot of people have very strong opinions that work on the main should only be done by a professional.

If Sara were concerned about it, she might be able to hire an electrician for 50-75 bucks to come look at her finished work to make sure it's safe.

I agree, interlocks look extremely simple to install. They are basically a piece of sheet metal fastened to the cover.

One thing for Sara to remember, if wires or breakers need to be moved in order to have an open space at the top of the main for your generator feed, make sure none of the wires/breakers share a neutral. If they do, make sure wires/breakers are on the same leg of the transformer, when moving them. That is, if a lead is on the left leg, move it to another slot on the left leg (not necessarily the left side, but the left leg) if the lead shares a neutral with another lead.

I think the reason most electricians don't want to install an interlock is that they've probably never done it. If they've always installed transfer switches that's what they're used to. They know how much time it will take them, how to bid them, where to get them, etc. Perhaps if you agreed to purchase the interlock and generator power cord inlet, you might find an electrician to do the job?

Below is a nice water-tight power cord inlet for $32. Notice it's a male plug. That's what you want so that when you make or purchase your power extension cord, it won't be a "suicide cord" (i.e. it will have a male and female end, vs. two male ends). The inlet is designed to be mounted in a box.

Here is a link that might be useful: RV power inlet

This post was edited by olpea on Sat, Feb 15, 14 at 11:11

I have read all your replies and really appreciate your warnings and suggestions. Now I am going to post some of follow up questions.

1) Grounding of the furnace

My generator's ground is connect to the ground prone of three prone plug(other two prone are not connected) through a 12 gauge wire and plug into an outside wall outlet. Is this good enough grounding for the generator? if I plug the furnace wire into generator, is this good enough grounding for the furnance?

2) why all this precaution when it comes to wiring for the furnace?

The electrical blanket can draw 1800W, space heater draws 1500W, even my coffe machine draws about 1400W, but they can be plugged in almost anywhere.

the gas funance peak draw is only about 2000 W, (steady draw is only a few hundred watts) not much more than the appliances mentioned above. Why all this precaution when it comes to wiring the furnace, like seperate circuit....,( I am not talking about suicide cord here)?

3) Oplea mentioned electricity generated by generator is of poor quality and can damage furnace. a 20 amp surge protector can prevent the damage to furnace from happenning, right? I looked into inverter generator before, it costs so much more;-(

I will post a picture of my furnace wiring later and may get some idea from you all about how to proceed.

thank you very much!

More questions later.

p.s. Olpea, just saw your last comment. I will read it more carefully and may have more questions for you and weedmeister

Whoa, you are connecting one of the genset outlets to the ground conductor in an outdoor outlet? I never would have dreamed of that. Better to use a ground electrode in the earth and ground the genset according to the directions.

I don't think that there is special concern for hooking up your furnace. The same concern would be there for hooking up anything inside your home to your genset.

There are several problems with power from portable generators. Voltage and frequency regulation are difficult with heavy loads turing off and on. The genset must maintain a constant RPM for frequency regulation, but must increase power instantly to do that. That is something that they can not do.

The shape of the sine wave seen in the simpler genset or inverter genset output is the other factor in power quality. In poor quality equipment, the wave is squared off,or otherwise distorted to a varying extent. Google [portable genset wave form] for some good images and discussion.

Although voltage surges can be problematic, electronic equipment, I am told, are not all that sensitive to power quality. Motors can be sensitive to wave form and overheat on poor quality power.

Ironically, for this discussion, electronic equipment can cause good power to somewhat go off the rails distorting the waveform. Large numbers of computers and, non incandescent, residential-grade lighting are notorious for that. A simple genet can't correct for that. On the other hand, an inverter might be able to. I really don't know, but it is an interesting possibility.

Cheap inverters often have clipped wave forms. Costly inverter generators are probably not in that same class. Common, non inverter, generators generally have a very good wave form.

A very significant advantage of inverter generators is that the motor speed varies with output. This results in much lower fuel consumption at low loads when most of your loads are turned off.

Sara, Ion beat me to it and gave you some good advice. I'll offer a bit more clarification on some questions you may have. It is a little difficult, as it's hard to discern how much knowledge you have in this area. I don't want to offer information which would be redundant to you.

"1) Grounding of the furnace

My generator's ground is connect to the ground prone of three prone plug(other two prone are not connected) through a 12 gauge wire and plug into an outside wall outlet. Is this good enough grounding for the generator? if I plug the furnace wire into generator, is this good enough grounding for the furnance?"

Assuming you are simply using a pigtail on your furnace, as Ion mentions, do not connect your generator to any of your house wiring system. I would treat the system as simply a portable generator system for NEC purposes. Namely, simply plug your three prong pigtail into a three prong extension cord and plug your three prong extension cord into your three prong recep on your generator. No ground rod is required.

Lastly, make sure the neutral in your generator is bonded to the equipment ground and the generator frame. Most generators are set up this way, but some aren't. It should say in your generator manual, but also do a check to make sure. You should see a wire bonding the generator to its frame. You should also see a jumper bonding the neutral to the equipment ground, but you may have to take off a cover to observe this.

Your generator should have GFCI for the 120V receptacles. You don't need any other ground protection than this.

Remember it's really the neutral that protects one against most faults which could cause electrocution. What most people call the "ground" is really a case ground (or equipment ground) which is ultimately "bonded" or connected to the neutral at some point. It's the "bond" of the neutral and case ground which really provides the fault protection when voltage leaks to the case. A ground rod doesn't really provide any protection in this sense.

Let me give a real world example (I hope I'm not offering info. redundant to you here.) Decades ago, before case grounds (or equipment grounds) were installed on refrigerators, people were sometimes electrocuted from them. What happened was this.

The refrigerator had a two prong plug - one for the lead, and one for the neutral (i.e. return current). The refrigerator would get old, wires would fray, or the motor would start leaking voltage. A lead wire would touch the case, or the motor would leak enough voltage the case/housing of the refrigerator would become energized.

Maybe from time to time one of the family members might notice the refrigerator would "shock" them. It wasn't a bad shock, because the impedance was too high for the return path from the case through the persons body to the neutral. In other words, the path of electricity wasn't a good connection. They had shoes insulating them, etc.

One day one of the family members, while getting some milk out of the refrigerator, spills some on the floor. It's early in the morning, so they're in their bare feet. They mop the milk up, but the floor is still wet. They grab the handle to put the milk back, but now the impedance is much lower (the combination of a wet floor and bare feet make a much better path for electricity). The current flowing through the person causes a constriction of the hand muscles. They can't let go of the handle. They can feel they are being electrocuted, but there is nothing they can do about it (by themselves). After a few moments, the same current causing constriction of the hand muscles makes the heart labor to keep it's rhythmic beat. After a short period, it stops beating altogether.

By installing a case/housing ground (i.e. the third prong on the plug) a low impedance grounding conductor provides a direct short in the circuit if there is a lead fault in the refrigerator housing. The path would be from the lead, shorted to the case, through the case ground wire, back the the main panel, where in the main panel, the neutral and the case ground buses are bonded (connected). This direct short will "pop" the breaker, or blow the fuse.

So long as the third prong on your pigtail is grounded to the case of the furnace, and the neutral and case ground are bonded on your generator, you won't be electrocuted from your furnace. You could still be electrocuted from your extension cord lying in a water puddle, or wet from rain if the outlet on your generator isn't gfci, but all newer generators are supposed to have gfci receps.

"Why all this precaution when it comes to wiring the furnace, like separate circuit?"

NEC requires all stationary appliances to be on their own circuit. So the main answer to your question is that it's code. The reason for the code requirement is to avoid people putting a lot of appliances on one circuit, causing the breaker to trip.

Let's say you have your refrigerator, deep freeze and furnace on one circuit. One day the breaker trips rendering all three appliances dead. It normally happens when you are on vacation, so you come back to your house with all your food spoiled and your pipes frozen/broken. As a bonus, the water thawed enough to run for three days, flooding your house.

NEC code allows an exception for any associated furnace equipment (humidifier, condensation pump) to be included on the same dedicated circuit as the furnace.

"Olpea mentioned electricity generated by generator is of poor quality and can damage furnace. a 20 amp surge protector can prevent the damage to furnace from happening, right?"

Unfortunately surge protectors really do very little in this regard (I'm referring to the surge power strips). A good one will prevent a major surges until the material inside is "consumed". This can happen with one surge. They won't prevent voltage drops. They also do nothing to correct sine wave distortion and frequency stability, which are also hard on electronics.

My main point was not to try to talk you into a new generator but to keep your generator lightly loaded if you need to run electronics like your furnace. That will at least provide more stable voltage.

Re: Inverter generators

When I mentioned inverter generators, I was thinking of high quality Yamaha or Honda inverters, which are pure sine wave inverters and known for producing the cleanest power. Ion is correct, cheap inverters produce a poor waveform (as do cheap non-inverter generators).

I disagree with Ion that electronics are not sensitive to power quality. I believe the opposite to be true.

This post is a lot longer than I intended. Didn't mean to write a book.

> NEC requires all stationary appliances to be on their own circuit.

Can you give me the reference to that in the NEC?

"NEC requires all stationary appliances to be on their own circuit."

That was just a general comment. I was trying to communicate to Sara that more than just the furnace must be on a dedicated circuit. But yes you are right, that statement was little too far. I should have said "a lot" of fixed appliances are required to be on their own circuit. Off the top of my head, Range, electric dryer, central air conditioner, furnace, microwave mounted over range, etc.

Some appliances aren't mandated, but it's just a good idea to have them on their own circuit.

To follow on, I don't think the NEC says anything but "follow the manufacturer's directions". If the furnace or refrigerator or dishwasher or ... says to place it on a dedicated circuit, then that is the rule you must follow.

" I don't think the NEC says anything but "follow the manufacturer's directions"

Range hoods

422.16(B)(4)Range Hoods.
Range hoods shall be permitted to be cord-and-plug connected with a flexible cord identified as suitable for use on range hoods in the installation instructions of the appliance manufacturer, where all of the following conditions are met:
(1) The flexible cord is terminated with a grounding- type attachment plug.
Exception: A listed range hood distinctly marked to identify it as protected by a system of double insulation, or its equivalent, shall not be required to be terminated with a grounding-type attachment plug.
(2) The length of the cord is not less than 18 in. and not over 36 in..
(3) Receptacles are located to avoid physical damage to the flexible cord.(4) The receptacle is accessible.
(5) the receptacle is supplied by an individual branch circuit.

This article would apply to over the stove mounted microwave as well as range hoods, since such microwave would also double as the range hood.

422.12 requires an individual branch circuit for the furnace.

210.11 requires a individual branch circuit for the laundry area

The following article can mandate a lot of things being on a dedicated by virtue of amp rating. For example, if disposer and dishwasher exceed 50% of the of the branch circuit amp rating, they must be on separate circuits. This can happen with newer more powerful units. Or a range and dryer sharing a circuit.

210.23 (A)
(1) Cord-and-Plug-Connected Equipment Not Fastened in Place. The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating.
(2) Utilization Equipment Fastened in Place. The total rating of utilization equipment fastened in place, other than luminaires, shall not exceed 50 percent of the branch circuit ampere rating where lighting units, cord-and-plug connected utilization equipment not fastened in place, or both, are also supplied.

Extremely useful, thorough and thoughtful thread. Thanks to all.

Wow, this thread is amazing! My electrical engineering husband wanted to make a suicide cord, and do the very thing that this thread is saying not to do. Of course, he finally decided for all the reasons that are stated that it wasn't a good idea. I'll have to study this thread a bit more to decide if we do a sub-panel or connect the generator to the main panel or put a plug on the end of the furnace cord and plug it into a dedicated outlet. But today in the Texas snow storm of 2021, this thread is very relevant!!!